No matter whether you are medium blonde or light brown: bleaching brightens the hair by up to nine shades. Special products for very dark hair from medium brown to black still create two to three shades - and even without an unwanted red cast. But how does that actually work? When bleaching, the cuticle layer is opened and a hydrogen peroxide cocktail in varying doses penetrates into the interior of the hair and breaks down the natural pigments to a greater or lesser extent. This process takes place over different levels of red and yellow.